The long term goal of this project is to understand the epidemiology of specific types of genital human papillomavirus infection (HPV) in young women. Although HPV is the most common sexually transmitted disease, and a major cause of morbidity and mortality, including venereal warts, squamous intraepithelial lesions (SILS), recurrent respiratory papillomatosis, and cancers of the cervix, vagina, vulva, penis, and anus, little is known about the virus as a sexually transmitted infectious agent. Results from the proposed study will provide fundamental epidemiologic measures of incidence, prevalence, and duration (key indicators of infectivity, persistence, progression, clearance,and transmissibility). The following specific aims will be pursued: 1. Define rates and determinants (e.g., condom use, frequency of intercourse, partner characteristics, co-infection, OC use) of acquisition of specific types of genital HPV. 2. Among women with incident infection by specific types of HPV, define the frequency, patterns, and determinants of persisting infection. 3. Among women with incident infection by specific types of HPV define the rate and predictors of squamous intraepithelial lesions (SILs), including high grade SIL. At present, 300 freshman university women (18-20 years of age) have been recruited to our on-going cohort study. These women have completed 1,858 examinations (average of 6.2 tri-annual exams/ subject). Interim analyses show that a total of sample of 600 women is needed to address important aims concerning risk of acquisition and natural history of specific types of genital HPV infections. Findings from this study will provide a basis for developing optimal strategies for primary prevention (e.g., immunization, condoms, or sexual behavior change) and secondary prevention (e.g., screening and treatment) of cervical cancer and other HPV associated epithelial lesions.